Numerous articles are designed for single or temporary use and have become commercially important in recent years. These articles are meant to be disposed of after being used once instead of being laundered or cleaned for re-use. Examples of garments of this general type are disposable diapers; adult incontinence garments; disposable bedsheets; disposable shower caps; garments intended for single use in hospitals such as surgical gowns, surgical hats and booties; and single use or disposable pajamas and the like intended to be worn by patients in the hospital for a short stay. Articles other than garments are also within this class, such as protective covers, dust covers, etc. Single use or disposable articles of this type are made of lightweight film or sheet materials such as thermoplastic films, non-woven fabrics of various materials such as thermoplastic or cellulosic fibers, paper, coated film or paper, and various composites of one or more of these types of materials such as disposable diapers which include, for example, layers of polyethylene and polypropylene which sandwich an absorbent material or fluff. These garment materials are distinguishable from textiles used to make a sewn garment or article which is intended for long-term use and subject to repeated laundering or dry cleaning.
Disposable articles of the type under consideration are economically feasible only when they can be manufactured at high production rates using techniques typical of converting film materials, such as heat sealing, sonic sealing, adhesive bonding, etc., instead of the sewing techniques customary with textile garments meant for longterm use. Even with the disposable articles, however, it is often desirable to shir the article, i.e., form an elasticized portion in order to provide a snug fit. In the case of disposable garments intended to be worn by human beings, for example, it may be necessary to provide a gown or similar item with elasticized wrists, or to produce a disposable diaper with elasticized waist portions and leg portions in order to provide a snug fit, or to provide disposable booties with an elasticized ankle-encircling portion. In the case of other products such as bed sheets and dust covers, a marginal portion that can fit snugly about an article with which the product is used is often required.
Because articles of this type need to be made at high production speeds, the formation of an elasticized portion by sewing in a strip of elastic material as is common in the production of textile garments is not practical.
Among the methods that have been developed or proposed in the art to form elasticized portions of disposable products are several which involve the use of heat, such as: (1) constructing the article of an oriented thermoplastic film and contact heating selected portions thereof to cause them to heat shrink and form integral elastic portions (see U.S. Pat. No. 3,245,407); (2) applying to the article a tape that is elastic at room temperature but rendered inelastic at elevated temperatures and heating selected portions of the tape to kill its elasticity (see U.S. Pat. No. 4,300,967 and published United Kingdom patent application No. 2,016,262); and (3) applying a tape of a material that is inelastic at room temperature but rendered elastic by the application of heat (see U.S. Pat. Nos. 3,639,917 and 3,912,565).
The method disclosure of U.S. Pat. No. 3,639,917 involves heating a garment section bearing heat recoverable elastomeric tape to temperatures in the range of 75.degree. C. to 150.degree. C. (167.degree. F. to 302.degree. F.) such as by use of a hot air gun, iron or an oven. U.S. Pat. No. 3,912,565 discloses forming an elasticized article by heating heat shrinkable uniaxially oriented polyurethane tape to a temperature slightly above its second order phase transition temperature, 100.degree. C. (212.degree. F.) being disclosed as an operable temperature; for this purpose, the patent states the heat may be applied by gas, such as hot air, or liquid.
In U.S. Pat. No. 3,912,565, the tape is disclosed as stretched by application of external heat, cooled at the stretched condition, then again heated by application of external heat to effect controlled heat shrinkage. In U.S. Pat. No. 3,639,917, block copolymers are irradiated, then expanded at elevated temperatures to achieve a new length, then cooled to maintain the copolymers at the new length. Subsequent reheating returns the copolymers to their original length.
Still other thermally-elasticizable materials, which include a preferred form useful in articles such as disposable diapers, can be oriented either by machine direction stretching or compression rolling to create potential elastic energy which can be recovered by heating to their activation temperature. Such materials, as are described in copending application Ser. No. 849,916, entitled Heat Shrinkable Elastomer, Method of Producing the Elastomer and Articles Utilizing the Elastomer now abandoned, assigned to the assignee of this application, have activation temperatures from about 125.degree. F. to about 230.degree. F.
As described above, it is imperative that this type of article be manufactured at high production rates in order to make them economically feasible. In this regard, it is advantageous to utilize a pressure sensitive hot melt adhesive to secure the tape to the article or garment. Such molten hot melt adhesives are formed at temperatures of from about 140.degree. C. to about 190.degree. C. (284.degree. F. to about 374.degree. F.). Since the activation temperatures of the thermally-elasticizable materials described above are below this range, and particularly the preferred form of heat recoverable elastomeric tape which has an activation temperature in the range of from about 125.degree. F. to about 230.degree. F., the molten hot melt adhesive can result in premature activation of the elastomeric tape which is undesirable.